1. Technical Field
The present invention relates to electronic compasses and more specifically to a method of orienting a flux-gate sensor.
2. Discussion
Normally, electronic compass systems employ a microprocessor to calculate vehicle headings based upon signals received from a magnetic flux-gate sensor. An example of a microprocessor based electronic compass can be found in U.S. Pat. No. 4,622,843 to Hormel, issued Nov. 18, 1986, entitled "Simplified Calibration Technique and Auto-Ranging Circuit for an Electronic Compass Control Circuit." This reference is hereby incorporated by reference.
The operation of the flux-gate sensors is also well documented. See for example, "Magnetic Field Sensor and Its Application to Automobiles," by Hisatsugu Itoh, February, 1980, SAE Paper 800123, pages 83-90; and "A Magnetic Heading Reference for the Electro/Fluidic Autopilot," Sport Aviation by Doug Garner, Part I, pages 19-26, November, 1981 and Part II, pages 20-32, and 51, December, 1981. These documents are hereby incorporated by reference.
Flux-gate sensors employ two perpendicular sense coils to sense the magnetic field of the earth. The flux-gate sensor also employs a primary winding which is used to periodically drive the core into saturation, thereby forcing the local magnetic field lines to jump in and out of the core. Voltages are induced in the sense coils, which are used to determine vehicle direction.
Traditionally, electronic compass systems determine direction by dividing the magnetic field strength in one coil by the magnetic field strength in the other coil and taking the arctangent of the quotient using a microcomputer. The problem with using the arctangent method is that the tangent is discontinuous at 90.degree. and 270.degree., approaching positive infinity from below 90.degree. and 270.degree. and negative infinity from above 90.degree. and 270.degree.. For flux-gate sensor mountings in which one sense coil is oriented longitudinally within a vehicle and the other sense coil is oriented transversely with a vehicle, this discontinuity causes jitter in displayed east and west headings.